In such cables, the oil is introduced into the cable during the process of manufacturing the electric cable or can be injected into the cable after manufacture, from one or more oil tanks. For some applications, the cable can be buried and at least one oil tank, connected to the underground cable, can be arranged at least one end of the cable, for example in an oil pressurization station.
Nevertheless, accidental oil leaks can occur through the outer sheath of the cable. These leaks can be due to ageing of the sheath, for example. It is then possible to detect a reduction in the oil level in one of the oil tanks, and it is then necessary to find the site of the leak and seal it off. Locating and repairing leaks are demanding operations that are complex to implement and ultimately always require significant earthworks which are generally carried out in an urban area.
A specific chemical agent can be injected into the oil, which diffuses into the cable oil and is released from the cable at the leak. The position of the leak can then be identified with a precision of a few meters only along the cable by detecting the emanations of the chemical agent through the soil. However, this method of locating a leak by chemical tracer has several drawbacks, namely:                It also requires the excavation of a portion of trench over a few meters in order to repair the leak.        It requires the use of a mass spectrometer type gas detector, which is expensive, bulky and complicated to use.        The gas released via the leak can be harmful to the environment.        